A typical gas turbine engine generally possesses a forward end and an aft end with its several core or propulsion components positioned axially therebetween. An air inlet or intake is at a forward end of the gas turbine engine. Moving toward the aft end, in order, the air intake is followed by a compressor, a combustion chamber, and a turbine. It will be readily apparent from those skilled in the art that additional components may also be included in the gas turbine engine, such as, for example, low pressure and high pressure compressors, and high pressure and low pressure turbines. This, however, is not an exhaustive list. A gas turbine engine also typically has an internal shaft axially disposed along a center longitudinal axis of the gas turbine engine. The internal shaft is connected to both the turbine and the air compressor, such that the turbine provides a rotational input to the air compressor to drive the compressor blades.
In operation, air is pressurized in the compressor and mixed with fuel in a combustor for generating hot combustion gases which flow downstream through turbine stages. These turbine stages extract gas energy from the combustion gases and converts such to mechanical energy. A high pressure turbine first receives the hot combustion gases from the combustor and includes a stator nozzle assembly directing the combustion gases downstream through a row of high pressure turbine rotor blades extending radially outwardly from a supporting rotor disk. In a two stage turbine, a second stage stator nozzle assembly is positioned downstream of the first stage blades followed in turn by a row of second stage rotor blades extending radially outwardly from a second supporting rotor disk.
In order to deliver fuel to the gas turbine engine, a single pump is generally utilized which pumps fuel for fuel burn, a fuel burn flow, and pumps fuel for valve actuation, a servo flow, and pumps fuel for mechanical actuation of external devices such as valves and stator positions, an actuation flow. These pumps are normally a fixed displacement type pump. However, the downside of a single pump, is that it generally wastes horsepower since such pump is sized to provide a higher flow than generally necessary. Additionally, the fuel may pass through a by-pass circuit which increases heat of the fuel and reduces the ability of the fuel to absorb other heat sources within the gas turbine engine.
With regard to the servo flow, it is not uncommon that valves and actuators become stuck in one position. When the valve changes to an unstuck position, this creates a high demand of fuel. In the instance where a single fixed displacement pump is utilized for both fuel burn flow and servo flow, the high demand may pull large amounts of fuel burn flow from the combustor, causing a flame-out of the engine.
As may be seen by the foregoing, it would be desirable to reduce the waste horsepower of the engine and it would be further desirable to reduce the heat increase of the fuel. Additionally, it would be highly desirable to reduce or eliminate the instances of flameout of the engine.